It is known in the art to prepare polyisoprene containing a high amount of cis-1,4 configuration using as the catalyst a mixture of a trialkylaluminum compound and a titanium tetrahalide. The high cis-1,4-polyisoprene has properties similar when vulcanized to those of vulcanized natural rubber and is a valuable general purpose rubber. However, the unvulcanized synthetic natural (SN) rubber has poorer green strength than natural rubber.
Canadian Pat. No. 664,208 teaches a very general two-stage process for reacting a polyolefinic monomer with a 1-monoolefinic hydrocarbon monomer.
U.S. Pat. No. 3,684,785 teaches a process for polymerizing isoprene using a catalyst consisting essentially of an organoaluminum compound and a titanium tetrahalide. The latter polymerization reaction is conducted in the presence of a small amount of ethylene not exceeding 8 parts by weight per 100 parts by weight of isoprene. It has been found that isoprene reacts preferentially to ethylene, particularly in the presence of a solvent. The heat of polymerization may also cause unreacted ethylene to vent from the reactor, creating a need for expensive refluxing and ethylene recovery equipment and resulting in poor conversion (e.g. about 20-25% by weight of ethylene to polymer). Moreover, processability (i.e. extrudability) of polymers made by the latter process may also be poor.
A new process is desired for polymerizing ethylene and isoprene to a product having satisfactory green strength and ethylene conversion efficiency together with excellent processability.